<chapter id="gbp.building">
    <title>Building packages from the &git; repository</title>
    <para>
    In order to build a &debian; package from the &git; repository, you use:
    &gbp-buildpackage;. This builds the upstream tarball (as will be described below) and
    invokes &debuild; to build the package. To use another build command, you
    can use the <option>--git-builder</option> option as described later in the manual,
    but &debuild; is nice since it can invoke <productname>lintian</productname>.
    During the development phase (when you're either not on the
    <emphasis>debian-branch</emphasis> or when you have uncommitted changes in
    your repository), you'll usually use:
    </para>
<programlisting>
&gbp-buildpackage; <option>--git-ignore-new</option>
</programlisting>
    <para>If &gbp-buildpackage; doesn't find a valid upstream tarball, it will
    create one by looking at the tag matching the upstream version. To change
    this behaviour, see the <option>--git-upstream-tree</option> option.
    </para><para>
    If you want to recreate the original tarball using the additional
    information from the <option>pristine-tar branch</option>, you have to
    specify the <option>--git-pristine-tar</option> option. This will make sure
    the upstream tarball matches exactly the one imported. Using this option is
    the recommended way of recreating the upstream tarball.
    </para>
    <para>Once you're satisfied with the build and want to do a release, you commit all
    your changes and issue:</para>
<programlisting>
&gbp-buildpackage; <option>--git-tag</option>
</programlisting>
    <para>This will again build the &debian; package and tag the final result after
    extracting the current version from the changelog. If you want &gpg;-signed
    tags, you can use the <option>--git-sign</option> and
    <option>--git-keyid</option> options. To save typing, these option can be
    specified via the configuration files. You can furthermore change the tag
    format used when creating tags with the <option>debian-tag</option>
    option; the default is <replaceable>debian/&lt;version&gt;</replaceable>.</para>
    <sect1 id="gbp.building.export">
    <title>Using a separate build dir</title>
    <para>Tools like &svn-buildpackage; use a separate build-area. To achieve a similar behaviour
    with &gbp-buildpackage;, use the <option>--git-export-dir</option> option:</para>
<programlisting>
&gbp-buildpackage; <option>--git-export-dir</option>=<replaceable>../build-area/</replaceable>
</programlisting>
    <para>This will export the head of the current branch to
    <replaceable>../build-area/package-version</replaceable> and build the
    package. If you don't want to export the current branch head, you can use
    <option>--git-export</option> to export any treeish object.  Here are some
    examples:</para>
<programlisting>
&gbp-buildpackage; <option>--git-export-dir</option>=<replaceable>../build-area</replaceable> <option>--git-export</option>=<replaceable>debian/0.4.3</replaceable>
&gbp-buildpackage; <option>--git-export-dir</option>=<replaceable>../build-area</replaceable> <option>--git-export</option>=<replaceable>etch</replaceable>
&gbp-buildpackage; <option>--git-export-dir</option>=<replaceable>../build-area</replaceable> <option>--git-export</option>=<replaceable>8caed309653d69b7ab440e3d35abc090eb4c6697</replaceable>
&gbp-buildpackage; <option>--git-export-dir</option>=<replaceable>../build-area</replaceable> <option>--git-export</option>=<replaceable>INDEX</replaceable>
&gbp-buildpackage; <option>--git-export-dir</option>=<replaceable>../build-area</replaceable> <option>--git-export</option>=<replaceable>WC</replaceable>
</programlisting>
    <para>The special argument <replaceable>INDEX</replaceable> exports the
    state of the current index, which can be used to include staged but uncommitted
    changes in the build. Whereas the special argument
    <replaceable>WC</replaceable> exports the current working copy as is.</para>
    <para>If you want to default to build in a separate build area, you can
    specify the directory to use in the <filename>gbp.conf</filename> file.
<programlisting>
[git-buildpackage]
# use a build area relative to the git repository
export-dir=../build-area
# to use the same build area for all packages use an absolute path:
#export-dir=/home/debian-packages/build-area
</programlisting>
    &gbp-buildpackage; will cleanup the build-area after a successful build. If
    you want to keep the build tree, use <replaceable>--git-no-purge</replaceable>.
    </para>
    </sect1>
    <sect1 id="gbp.building.hooks">
    <title>Invoking external programs</title>
    <para>
    Besides the commands for cleaning the package build dir
    (<option>cleaner</option>) and building the package
    (<option>builder</option>), you can also invoke hooks during the package
    build: immediately before a build (<option>prebuild</option>),
    after a successful build (<option>postbuild</option>), and after
    creating a tag (<option>posttag</option>). Typical applications are running
    <productname>lintian</productname> or pushing changes into a remote
    repository.
    </para>
    <sect2 id="gbp.building.lintian">
    <title>Running lintian</title>
	<para>&gbp-buildpackage; exports several variables into the
	<option>posttag</option>'s environment (for details see the <xref
	linkend="man.gbp.buildpackage"/>).
	To invoke &lintian;, we need to tell it where to find the changes file:
<programlisting>
&gbp-buildpackage; <option>--git-postbuild</option>=<replaceable>'lintian $GBP_CHANGES_FILE'</replaceable>
</programlisting>
        To call &lintian; automatically after each successful build, add:
<programlisting>
<option>postbuild</option>=<replaceable>lintian $GBP_CHANGES_FILE</replaceable>
</programlisting>
	to your <filename>.gbp.conf</filename>.
    </para>
    </sect2>
    <sect2 id="gbp.building.push">
    <title>Pushing into a remote repository</title>
	<para>If you want to push your changes automatically after a successful build and tag,
	you can use &gbp-buildpackage;'s posttag hook. A very simple invocation would look like this:
<programlisting>
&gbp-buildpackage; <option>--git-tag</option> <option>--git-posttag</option>=<replaceable>"git push &amp;&amp; git push --tags"</replaceable>
</programlisting>
	This assumes you have set up a remote repository to push to in
        <filename>.git/config</filename>.</para>

	<para>Usually, you want to make sure you don't push out any
        unrelated changes into the remote repository. This is handled by the
        following hook which only pushes out the created tag to where you pulled
        from and also forwards the corresponding remote branch to that position:
<programlisting>
#!/bin/sh -e
#
# gbp-posttag-push: post tag hook to push out the newly created tag and to
# forward the remote branch to that position

if ! REMOTE=$(git config --get branch."${GBP_BRANCH}".remote); then
    REMOTE=origin
fi

if [ "$GBP_TAG" ]; then
     echo "Pushing $GBP_TAG to $REMOTE"
     git push "$REMOTE" "$GBP_TAG"
else
     echo "GBP_TAG not set."
     exit 1
fi

if [ "$GBP_SHA1" ] &amp;&amp; [ "$GBP_BRANCH" ]; then
    git push "$REMOTE" "$GBP_SHA1":"$GBP_BRANCH"
else
    echo "GBP_SHA1 or GBP_BRANCH not set."
    exit 1
fi
echo "done."
</programlisting>
	<envar>GBP_TAG</envar>, <envar>GBP_SHA1</envar>
        and <envar>GBP_BRANCH</envar> are passed to the hook via the
        environment. To call this hook automatically upon tag creation, add:
<programlisting>
<option>posttag</option>=<replaceable>"gbp-posttag-push"</replaceable>
</programlisting>
	to your <filename>.gbp.conf</filename> and make sure <filename>gbp-push</filename>
	is somewhere in your <envar>$PATH</envar>. On &debian;
	systems, a more complete example can be found in
	<filename>/usr/share/doc/examples/git-buildpackage/examples/gbp-posttag-push</filename>.
    </para>
    </sect2>
    <sect2 id="gbp.building.postexport">
    <title>Running postexport hook</title>
    <para>&gbp-buildpackage; exports several variables into the
	<option>postexport</option>'s environment (for details see
	the <xref linkend="man.gbp.buildpackage"/>). The motivation
	for the postexport action is to allow further adjustment of
	the sources prior to building the package. A typical use case
	scenario is to allow creating multiple source and binary
	packages from one &debian; branch, e.g. the bootstrap gcc and
	in the next stage the full gcc.
    </para>
    <para>The postexport action postpones the creation of the
      upstream tarball, so that the metadata for creating it is
      already present in the exported source tree. The example
      postexport script below (<filename>crosstoolchain-expand.sh</filename>)
      expands changelog, lintian override files, rules and control files
      according to an environment variable <envar>PKG_FLAVOR</envar>.
    </para>

    <para>Sample <filename>gbp.conf</filename> - enables source tree export
    by specifying the export directory:
    </para>
<programlisting>
[git-buildpackage]
# use a build area relative to the git repository
export-dir = ../build-area
# disable the since the sources are being exported first
cleaner =
# post export script that handles expansion of &debian; specific files
postexport = crosstoolchain-expand.sh
</programlisting>


<para>Sample postexport script: <filename>crosstoolchain-expand.sh</filename></para>
<programlisting>
#!/bin/sh
#
# Purpose: this script is intended for creating multiple source and
# binary Debian packages from one source tree. It can be used in
# conjunction with git-buildpackage that support a postexport hook
#
# A typical use is preparing a bootstrap gcc package that is needed
# for building newlib and then preparing a full gcc package from the
# same source tree. The user may specify the package flavor via
# PKG_FLAVOR environmental variable. 
#
#
# The script expands/processes the following files:
#
# - changelog.tmpl is converted to standard Debian changelog
#
#
# - all binary package lintian override template files are expanded
#   and renamed to the requested package flavor
#
# - source package lintian override template file is expanded and
#   renamed
#
# - rules.$PKG_FLAVOR and control.$PKG_FLAVOR are renamed to rules and
#   control resp.


# the template string has been carefully chosen, so that
# e.g. changelogs that refer to the source package can still be
# processed by dch/git-dch resp.
TMPL_STR=-XXXXXX

# by default replace string for the template is empty
REPLACE_STR=

if [ -n "$PKG_FLAVOR" ]; then
    REPLACE_STR=-$PKG_FLAVOR
fi

REPLACE_EXPR="s/$TMPL_STR/$REPLACE_STR/g"


# actual processing of relevant files
cd debian

# expand the template changelog
# remove the symlinked version
rm changelog
chglog_tmpl=changelog.tmpl
[ -f "$chglog_tmpl" ] || {
    echo "Missing changelog template (debian/$chglog_tmpl)"
    exit 1
}
cat changelog.tmpl | sed -e "$REPLACE_EXPR" > changelog
rm changelog.tmpl

# process binary package lintian overrides - each override must match
# its package name
for f in *.lintian-overrides.tmpl; do
    outfile=${f%.tmpl}
    [ -f "$f" ] || {
	echo "Missing lintian override files for binary packages"
	exit 1
    }
    cat $f | sed -e "$REPLACE_EXPR" > ${outfile/$TMPL_STR/$REPLACE_STR}
    rm $f
done

# process the only source package lintian override
source_lintian=source/lintian-overrides.tmpl
cat $source_lintian | sed -e "$REPLACE_EXPR" > ${source_lintian%.tmpl}
rm $source_lintian

# rules and control file are package flavor specific
[ -f rules.$PKG_FLAVOR ] &amp;&amp; mv rules.$PKG_FLAVOR rules
[ -f control.$PKG_FLAVOR ] &amp;&amp; mv control.$PKG_FLAVOR control
rm -f rules.* control.*

exit 0
</programlisting>
    </sect2>
    </sect1>
</chapter>
